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HANDBOOK OF PHYSIOLOGY. 



Each crus cerebri contains among its fibres a mass of gray substance, 

 the locus niger. 



Functions. With regard to their functions, the crura cerebri may be 

 regarded as, principally, conducting organs: the crus fa conducting 

 chiefly motor and the tegmentum sensory impressions. As nerve-centres 

 they are probably connected with the functions of the third cerebral 

 nerve, which arises from the locus niger, and through which are directed 

 the chief of the numerous and complicated movements of the eyeball. 

 The crura cerebri are also in all probability connected with the co-ordi- 

 nation of other movements besides those of the eye, as either rotatory 

 or disorderly movements result after section of either of them. 



Lesion of one crus is followed by motor and sensory, partial or com- 



1ft 



FIG. 340. Diagram of the motor tract as shown in a diagrammatic horizontal section through the 

 Cerebral hemispheres, Crura, Pons, and Medulla. Fr., frontal lobe; Oc., occipital lobe; AF., ascend- 

 ing frontal; AP., ascending parietal, convolutions; PCF., pre-central fissure in front of the ascend- 

 ing frontal convolution; FR., fissure of Rolando; IPF , inter-parietal fissure, a section of crus is let- 

 tered on the left side. SN., substantia nigra ; Py.. pyramidal motor fibre, which on the right is shown 

 as continuous lines converging to pass through the posterior limb of 1C., internal capsule (the knee 

 or elbow of which is shown thus*) upwards into the hemisphere and downwards through the pons 

 to cross the medulla in the anterior pyramids. (Gowers.) 



plete paralysis of the opposite side of the body and paralysis of the third 

 nerve of the same side as the lesion. 



E. The Corpora Quadrigemina. 



The corpora quadrigemina (from which, in function, the corpora 

 geniculata are not distinguishable) are the homologues of the optic lobes 

 in Birds, Amphibia, and Fishes, and may be regarded as the principal 

 nerve-centres for visual sensations. 



Functions. (1) The experiments of Flourens, Longet, and Hertwig 

 show that removal of the corpora quadrigemina wholly destroys thepoiver 



